In mining operations, it is necessary to monitor what is being mined to determine the grade of ore. Mining costs are expensive. If the grade of ore is not high enough to justify the mining expense, the mine may be shut down until less expensive methods for mining can be discovered or new mining sites are found. Having mining operations follow the high grade ore deposits is imperative. To do this, representative samples of the ore being mined must be assayed. Since assay facilities are typically not located at the mining site, the ore samples must be collected, transported to the assay facility, and prepared for assay.
Likewise, exploration for metals and minerals requires the monitoring of ore samples. However, the collection and transportation of exploration samples create problems that can be significantly different from the problems encountered with the collection and transportation of mine samples. For example, exploration samples may result from a drilling process known as "reverse circulation" drilling which is deep drilling where water is used to bring the sample to the surface. With this process, samples have been collected every five feet in plastic buckets and transferred as a slurry to clear plastic bags and sealed using a wire tie and labeled with a marking pen and a paper tag. Typically, the samples have been left standing in the field until the liquid and solids separated. The bag was then pierced above the solids layer to drain the standing water out onto the ground. Fine particles were often poured onto the ground.
The collection of mine samples presents different requirements and needs. Mine samples are collected at the blast hole drills. Surveyors lay out each row of drilling and assign sample numbers to each of the holes to be drilled Typically, the driller places a sample bag in a 4" diameter PVC pipe which is part of a sample catcher. The catcher is lowered through the drill deck prior to drilling and is raised before any sub-drilling is required. The sample is recovered and tossed off the platform to be collected by the sampler and the drill is advanced to the next hole.
The mine sample is collected using a relatively dry process compared to reverse circulation drilling. Thus, the bag does not need to be a filter media for separation of the sample from the water. However, the blast hole cuttings can be larger and sharper than the exploration cuttings and the volume of cuttings required for assay is less.
In the past, the collection, transportation, and preparation of ore samples have been done in cotton "sand bags." These types of bags have had problems in maintaining sample integrity. Leakage of fine particles in the ore sample through the seam of the bag or through the pores in the material from which the bag was constructed have presented particular problems. Later, permeable olefin bags were tested. The permeable olefin bags would automatically drain through the pores in the bag and could be air dried in the field. However, use of these bags raised concerns that losses of fine sample material through the pores would bias the assay. During preliminary testing of such bags, it has been determined that a significant percent of the sample material can be lost when a slurry is allowed to drain from the bag. The material loss has been primarily through the seam of the bag. In one instance, the material lost contained over fifty percent (50%) of the gold, thus significantly down-grading the assay of the sample remaining in the bag.
Plastic bags have also been used, but they were found unsuitable for most uses. Because most plastic bags have a tacky surface, a relatively high sample loss through fines sticky to the bag has been experienced.
In order to address several of the problems with ore sample bags, various improvements have been made. Seams for the bags are folded or lapped before sewing to eliminate leakage through the seam. Also, bags with draw strings have been developed. Additionally, bags constructed of various materials have been used.
A degree of porosity is desirable to allow for drying, but the mesh size of the pores in the bag must be sufficient to restrict passage therethrough by fine particles of the sample. Materials from which ore sample bags are constructed must also be flexible and durable. Materials that have been found to be suitable include a material made by DuPont and sold as Tyvek.RTM. and a canvas-like bone velour material ranging from 270 to 400 mesh.
Equally important in the use of ore sample bags is the need to identify and track the ore sample during the entire process of collection, transportation, preparation, and the assay. Identification and tracking can be a very involved. During exploration, for example, as many as a thousand samples a day may be taken on a predetermined grid pattern. In the past, each sample was identified manually by marking each bag using a pen and label and tracked by manually logging each sample as it passed through each step in the process. However, such identification and tracking is labor intensive and subject to human error, frequently resulting in confusion of samples. Today, it is quite common for a three label technique to be used to increase tracking integrity. With this technique, one label bearing identification indicia is placed on a stake driven into the ground at the location where the sample is taken. A second label is attached to the outside of the bag, and a third label is placed inside the bag. The redundancy is needed to assure identification and tracking capability if one or more of the labels are destroyed during collection, transportation, preparation, or the assay.
As computer technology made bar code reading more feasible, labels with bar codes were attached to the bags. A corresponding human readable identification was written on each bag. However, various problems have been encountered in using bar code labels on ore sample bags. Solvents used in drilling attacked the bar code labels causing significant errors in the logging of samples. Also, writing of human readable identification on each bag was time consuming and subject to human error. Unfortunately, the hand-written identification could be obliterated during the typical rough handling of the ore sample bag.
In order to solve some of the problems with bar coded labels various improvements were introduced. The bar coded labels were preplanned with computer generated tracking indicia. The bar codes were photo composed on polyester stock and a special UV resistant over laminate has been applied. This made the labels one hundred percent scannable, eliminated redundancy and missing numbers, and made the labels resistant to the solvents used during drilling. To again reduce labor costs, bar coded labels are now sewn into the seam of the bag when the bag is constructed, which eliminates the application of the label to the bag in the field. However, heretofore, if a bag was handled roughly such that the tag was torn from the bag and the hand-written indicia was obscured, the bag could not be identified or tracked properly.
Despite all of the efforts to improve ore sample bags to reduce labor costs, reduce ore sample loss, and to assure accuracy in identification and tracking, several problems remain. When bags with drawstrings are tied off in the field, they are frequently difficult to open without cutting the drawstring. If the drawstring is cut, the bag cannot be reclosed without introducing some other means of closure. Additionally, bags closed by gathering the material at the top of the bag such as by drawstring, tying off the bag, or the use of wire ties cause the bag to bunch and not lay as flat as the bag would if the top is not gathered. A bag that can lay relatively flat in a drying oven takes less time for the sample to dry.
The foregoing needs and problems indicate that it would be a significant advance in the art if an ore sample bag can be constructed which can be opened and closed using a single reusable means for closure. It would reduce costs and be a further advance to provide a durable, reliable, and reusable ore sample bag that will maintain sample integrity so that a more accurate representative sample may be assayed.
It would also be a significant advance to provide a labeling system for identification and tracking of ore samples that is more reliable, more cost effective, and less likely to result in errors. A system that avoids redundancy and human error while providing labels that are both scannable and human readable would be particularly advantageous.